Fused deposition modelling (FDM) is a layer-manufacturing technology that has been increasingly popular in last years. This increment can be explained due to their Ability in field of manufacturing in order to allow us to make any kind of geometry in a satisfactory time. This method is based on using heat extrusion of thermoplastics wire. The FDM process involves heat and mass transfer, rapid cooling, repetitive heating and cooling coupled with mechanical loading and phase changes and Parts are constructed by the sequential deposition of material layers. When the deposition process involves temperature gradients, thermal stresses will develop. Thus, parts made by FDM process deviate from the designed geometry. Most severe form inaccuracies such as curl and warping are attributed to the residual stress accumulations during prototype fabrications. During FDM process, the Acrylonitrile Butadiene Styrene (ABS) polymer experiencing multiple phases including solid, melting and re-solidification. The effect of temperature and time of loading on material properties is high because of the viscoelastic nature of the polymer material. In this thesis, the temperature distribution, residual stress and part distortion in fused deposition modeling (FDM) processes is studied, and the behavior of the material during the process is evaluated. In the transition temperature region, the behavior of thermoplastic polymers are viscoelastic materials. The viscoelastic parameters are obtained from static tensile test. The coefficient of bulk and shear modulus of ABS material are obtained by non-linear curve fitting in MATLAB software. A finite element analysis model using element activations has been developed to simulate the mechanical and thermal phenomena in FDM and further used for temperature distribution, residual stress and part distortion simulations. When the temperature distribution is calculated, the result is shared as the load to analysis the strain and stress distributions. The maximum residual stress was observed at the bottom surface of the part, which is in contact with the platform. The magnitude of the residual stresses increases as expected when the process continues. This resulted from the number of heating-cooling cycles, and the time interval between the cycles. The results obtained by finite element simulation are compared with the experimental reading of temperature and distortion. There was good agreement between the model predictions and the experimentally observed values of temperature and distortion. This correspondence shows that the model correctly describes the behavior of ABS materials and for a variety of thermoplastic polymers, can be generalize it. Keywords : Additive manufacturing, FDM, Viscoelastic, Prony Serious, Finite element simulation, Residual stress, Distortion